The U.S. Food and Drug Administration warned General Mills Inc. (GIS) that labeling that makes certain health claims for Cheerios whole-grain oat cereal contains "serious violations" of agency rules.

In a May 5 warning letter sent to the company and posted on the FDA's Web site Tuesday, the agency said statements made on the product's label about Cheerios' ability to lower cholesterol cause the product to be a drug under agency regulations.

The FDA said claims made on the product's package stating that Cheerios is clinically proven to lower cholesterol can only be made if the product were to be approved as a drug. The product label says Cheerios can lower cholesterol by 4% and cited a clinical study involving the product as part of a diet low in saturated fat and cholesterol. The FDA said Cheerios "can't be legally" marketed with claims it lowers cholesterol by a certain percentage without an approved new drug application.

The FDA also took issue with a company-sponsored Web site mentioned on the Cheerios box. The Web site discusses the benefits of eating whole grains, but the FDA said some of the health claims about reducing cancer and heart-disease risk don't comply with agency rules regarding health claims for whole grains.

In a statement, General Mills spokesman Tom Forsythe said, the message saying "lower your cholesterol 4% in 6 weeks" has been featured on the box for more than two years and claims about heart health have been FDA-approved for 12 years.

"The scientific body of evidence supporting the heart health claim was the basis for FDA's approval of the heart health claim, and the clinical study supporting Cheerios' cholesterol-lowering benefit is very strong," he said. Forsythe said the company, however, would work with the FDA to reach a solution on product labeling.

The FDA said General Mills must "promptly" correct the violations outlined in the letter or the agency could take enforcement action, such as seizing products.

-By Jennifer Corbett Dooren, Dow Jones Newswires; 202-862-9294; jennifer.corbett@dowjones.com